This invention relates to reduction in air pollution, and more particularly to particulate filtration of vehicle exhaust gases.
Air cleanliness has become societally important, and government regulations are in force for controlling toxic discharge from factories, industries, and from aircraft and other vehicles. Car exhaust regulations have resulted in improvements in emissions of oxides of nitrogen, hydrocarbons, and carbon monoxide, as well as emissions of so-called greenhouse gases. Truck and bus emissions are subject to regulations which are becoming more stringent. In addition, fuel economy has become more important in recent years, as worldwide demand for petroleum-based liquid hydrocarbon fuels causes increases in fuel prices. Increased fuel economy, in turn, tends to reduce exhaust emissions per mile of travel.
One approach to reduced emissions and improved fuel economy is the use of electrically driven automobiles, trucks and buses. However, electrically driven vehicles tend to have relatively short range, and are difficult to heat and air-condition, and may not be all that economical. Another technique for overcoming some of the problems associated with electrically driven vehicles is the use of hybrid internal-combustion/electrical drive, in which an internal combustion engine drives an electrical generator to produce electricity for recharging batteries, and the vehicle drive is provided by an electrical motor powered at least in part by the batteries. So-called ultracapacitors are expected to approach the performance of electrochemical batteries for electrical storage, and may find use in the future.
An advantage of hybrid electric vehicles is that the internal combustion engine which generates the electrical power is decoupled from the vehicle drive wheels, so the engine may be run at a speed which is independent of the vehicle speed, at least in the short term. This, in turn, allows the engine to be operated at a speed selected for superior fuel economy, reliability, andor emission control.
Improved techniques are desired for reducing the emissions of engines used in vehicle applications.
A method according to an aspect of the invention is for cleaning a regenerative particulate filter or xe2x80x9ctrapxe2x80x9d associated with a particulate-generating internal combustion engine. The method includes the step of passing exhaust gases from the engine through a regenerative particulate filter for removing particulate matter from the filter effluent or output gases. A back-pressure signal is generated. The back-pressure signal is representative of the average back pressure of the filter. The step of generating a back pressure signal representing the average back pressure-may be performed by generating a series of instantaneous back-pressure signals, and integrating the signals, in known manner, to produce an average. When the back-pressure signal reaches a predetermined threshold, the engine is set to or toward a speed in the lower portion of its range, and the engine loading is increased, whereby the temperature of the engine exhaust gases tends to increase, and the temperature of the filter also tends to increase, thereby aiding in regenerating the filter.
In a particular mode of the method of the invention, the step of increasing the loading comprises the step of adjusting an electrical-energy-producer powered by the engine for generating increased electrical energy, and coupling the increased electrical energy to an electrical load. In a version of this mode, the step of coupling the increased electrical energy includes the step of coupling at least a portion of the increased electrical energy to a resistive dissipating device. An embodiment of a resistive dissipating device is a discrete resistor. In another version of this mode, the step of coupling the increased electrical energy to an electrical load includes the step of coupling at least a portion of the increased electrical energy to a traction energy storage device, such as a battery or ultracapacitor.
In a particularly advantageous mode of the invention, a second threshold is provided, which is at a lower level of back pressure than the first-mentioned threshold. Above this threshold value, the traction energy storage device is charged toward a setpoint which represents a lower energy level, so that energy attributable to the increased load can be stored in the traction storage device without overcharging. In a further embodiment of the invention, the step of controlling the increased loading is accomplished under at least partial control of the filter temperature.